There are exceptions to the paradigm that reductions in smooth muscle tone represent reversal of activation; lowering myoplasmic calcium and inactivation of MLCK and crossbridge dephophorylation. Nitric oxide (NO) is a ubiquitous neuroendocrine, paracrine and autocrine inhibitory signal that is know to relax smooth muscle by lowering the myoplasmic calcium concentration. Urogenital smooth muscles typically have a rich inhibitory innervation which generates NO. This application proposes that NO release induces a calcium-ion and crossbridge independent active component of relaxation which accelerates the inherently slow relaxation characteristic of visceral smooth muscle. The five specific aims are to (1) characterize the calcium ion independent component of relaxation in several urogenital smooth muscle tissues, (2) test the hypothesis that increases in cGMP and activation of protein kinase G in response to NO are temporally regulated and quantitated with the active component of relaxation, (3) test the hypothesis that active relaxation is a mechanism to abolish latch and speed relaxation, (4) test the hypothesis that increases in cGMP are are temporally regulated and quantitatively correlated with changes in phosphorylation of HSP20 that inhibits force generation and (5) test the hypothesis that phosphorylation of HSP20 acts as a thin filament "off switch" that prevents force generation by blocking the attachment of phosphorylated crossbridges.